Transmit/receive antenna system having offset feed points for high isolation

Abstract

Provided is an antenna system with high isolation. The high-isolation antenna has transmission ports of a transmission antenna and reception ports of a reception antenna highly isolated from each other by using quadrature hybrid couplers. The antenna system includes: a transmission antenna having two feed points for transmitting signals; a reception antenna having two feed points for receiving signals; a transmission hybrid coupler which is connected to the two feed points of the transmission antenna and transmits transmission signals which have a phase difference of 90° with each other; and a reception hybrid coupler which is connected to the two feed points of the reception antenna and receives reception signals which have a phase difference of 90° with each other. The signals leaking from the two feed points of the transmission antenna to the two feed points of the reception antenna are offset.

1. An antenna system with a transmission part and a reception part highly isolated from each other, comprising:
 a transmission antenna for transmitting signals, the transmission antenna having a first feed point a and a second feed point b; 
 a reception antenna for receiving signals, the reception antenna having a first feed point c and a second point d; 
 a transmission hybrid coupler which is connected to the first feed point a and the second feed point b of the transmission antenna and transmits transmission signals which have a phase difference of 90° from each other; and 
 a reception hybrid coupler which is connected to the first feed point c and the second feed point d of the reception antenna and receives reception signals which have a phase difference of 90° from each other, 
 wherein a transmission coefficient from any one of the first feed point a and the second feed point b of the transmission antenna to any one of the first feed point c and the second feed point d of the reception antenna is substantially the same as a transmission coefficient from the other of the first feed point a and the second feed point b of the transmission antenna to the other of the first feed point c and the second feed point d of the reception antenna, so that signals leaking from the feed points a and b of the transmission antenna to the feed points c and d of the reception antenna are offset. 
 
     
     
       2. The antenna system as recited in  claim 1 , further comprising:
 a ground body of a cavity structure which has apertures in main beam directions of the transmission and reception antennas and partially surrounds the transmission and reception antennas. 
 
     
     
       3. The antenna system as recited in  claim 1 , wherein the transmission coefficient from the first feed point a to the second feed point d is substantially the same as the transmission coefficient from the second feed point b to the first feed point c with respect to an equivalent 4-port network scattering coefficient, which represents coupling among the first feed points a and c and the second feed points b and d. 
     
     
       4. The antenna system as recited in  claim 3 , wherein the transmission hybrid coupler includes two ports T 1  and T 2  for supplying transmission signals respectively to the first feed point a and the second feed point b of the transmission antenna, and the reception hybrid coupler includes two ports R 1  and R 2  for receiving reception signals respectively from the first feed point c and the second feed point d of the reception antenna, and
 a transmission coefficient from the port T 1  to the port R 2  is substantially the same as a transmission coefficient from the port T 2  to the port R 1  with respect to an equivalent 4-port network scattering coefficient composed of the four ports T 1 , T 2 , R 1  and R 2 . 
 
     
     
       5. The antenna system as recited in  claim 4 , wherein when the port T 1  is used as a transmission port, the port R 2  is used as a reception port; and when the port T 2  is used as a transmission port, the port R 1  is used as a reception port. 
     
     
       6. The antenna system as recited in  claim 5 , wherein the ports T 2  and R 1  are unused ports when the port T 1  is used as the transmission port and the ports T 1  and R 2  are unused ports when the port T 2  is used as the transmission port, and wherein the unused ports of the couplers include matched loads attached thereto. 
     
     
       7. The antenna system as recited in  claim 1 , wherein the transmission coefficient from the first feed point a to the first feed point c is substantially the same as the transmission coefficient from the second feed point b to the second feed point d with respect to an equivalent 4-port network scattering coefficient, which represents coupling among the first feed points a and c and the second feed points b and d. 
     
     
       8. The antenna system as recited in  claim 7 , wherein the transmission hybrid coupler includes two ports T 1  and T 2  for supplying transmission signals respectively to the first feed point a and the second feed point b of the transmission antenna, and the reception hybrid coupler includes two ports R 1  and R 2  for receiving reception signals respectively from the first feed point c and the second feed point d of the reception antenna, and
 a transmission coefficient from the port T 1  to the port R 1  is substantially the same as a transmission coefficient from the port T 2  to the port R 2  with respect to an equivalent 4-port network scattering coefficient composed of the four ports T 1 , T 2 , R 1  and R 2 . 
 
     
     
       9. The antenna system as recited in  claim 8 , wherein when the port T 1  is used as a transmission port, the port R 1  is used as a reception port; and when the port T 2  is used as a transmission port, the port R 2  is used as a reception port. 
     
     
       10. The antenna system as recited in  claim 9 , wherein the ports T 2  and R 2  are unused ports when the port T 1  is used as a transmission port and the ports T 1  and R 1  are unused ports when the port T 2  is used as the transmission port, and wherein the unused ports of the couplers include a matched load attached thereto. 
     
     
       11. The antenna system as recited in  claim 1 , wherein the transmission coefficient from the feed first point a to the second feed point d is substantially the same as the transmission coefficient from the second feed point b to the first feed point c with respect to an equivalent 4-port network scattering coefficient, which represents coupling among the first feed point a and c and the second feed points b and d. 
     
     
       12. The antenna system as recited in  claim 11 , wherein the transmission hybrid coupler includes two ports T 1  and T 2  for supplying transmission signals respectively to the first feed point a and the second feed point b of the transmission antenna, and the reception hybrid coupler includes two ports R 1  and R 2  for receiving reception signals respectively from the first feed point c and the second feed point d of the reception antenna, and
 a transmission coefficient from the port T 1  to the port R 2  is substantially the same as a transmission coefficient from the port T 2  to the port R 1  and a transmission coefficient from the port T 1  to the port R 1  is substantially the same as a transmission coefficient from the port T 2  to the port R 2  with respect to an equivalent 4-port network scattering coefficient composed of the ports T 1 , T 2 , R 1  and R 2 . 
 
     
     
       13. The antenna system as recited in  claim 12 , wherein the transmission coefficient from the port T 1  to the port R 2  is larger than the transmission coefficient from the port T 1  to the port R 1 , and
 wherein a pair of a transmission port and a reception port is selected from the group consisting of a pair of the transmission port T 1  and the reception port R 1  and a pair of the transmission port T 2  and the reception port R 2 . 
 
     
     
       14. The antenna system as recited in  claim 12 , wherein the transmission coefficient from the port T 1  to the port R 2  is smaller than the transmission coefficient from the port T 1  to the port R 1 , and
 wherein a pair of a transmission port and a reception port is selected from the group consisting of a pair of the transmission port T 1  and the reception port R 2  and a pair of the transmission port T 2  and the reception port R 1 . 
 
     
     
       15. An antenna system with a transmission part and a reception part highly isolated from each other, comprising:
 transmission and reception antennas for providing signal transmission and reception, respectively, the transmission antenna having two feed points a and b and the reception antenna having two feed points c and d; and 
 transmission and reception hybrid couplers for dual feeding to the transmission and reception antennas, respectively, 
 wherein a transmission coefficient from any one of the feed point a and the feed point b of the transmission antenna to any one of the feed point c and the feed point d of the reception antenna is substantially the same as a transmission coefficient from the other of the feed points a and b of the transmission antenna to the other of the feed points c and d of the reception antenna, so that signals leaking from the two feed points a and b of the transmission antenna to the two feed points c and d of the reception antenna are offset by each other. 
 
     
     
       16. The antenna system as recited in  claim 15 , wherein each of the antennas is any one selected from the group consisting of a circular patch, a square patch, and a polygonal patch. 
     
     
       17. The antenna system as recited in  claim 15 , wherein the transmission hybrid coupler includes two ports for supplying transmission signals to the two feed points a and b of the transmission antenna, respectively, and the reception hybrid coupler includes two ports for receiving reception signals to the two feed points c and d of the reception antenna, respectively, and
 wherein a transmission coefficient from any one port between the two ports of the transmission hybrid coupler to any one port between the two ports of the reception hybrid coupler is substantially the same as a transmission coefficient from the other port of the transmission hybrid coupler to the other port of the reception hybrid coupler. 
 
     
     
       18. The antenna system as recited in  claim 15 , wherein the dual feeding is direct feeding.